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si s2

s

Fig. 33-1 Ts Diagram of Reversed Carnot Cycle.

Fig. 33-1 Ts Diagram of Reversed Carnot Cycle.

Qin = Heat added to the cycle (heat removed) = area 1-2-b-a-1

Wcycie = Net work supplied to the cycle = Qout — Qjn = area 1-2-3-4-1

As can be seen from the Ts diagram, in the reversed cycle, area 1-2-3-4 measures the net work supplied to the cycle and area 1-2-b-a represents the heat removed from the colder region. Note that points a and b are at absolute zero. The cycle processes described above are represented diagrammatically as a vapor refrigeration cycle in Figure 33-2. It operates in the following manner:

• Refrigerant enters the evaporator at State 1 as a two-phase liquid-vapor mixture. In the evaporator, heat from the conditioned space or process load is transferred to the refrigerant.

• Evaporation of refrigerant (States 1 to 2) occurs as heat transfer from the conditioned space or process load causes the refrigerant to undergo a phase change from liquid to vapor. This process occurs at a constant temperature TL and constant pressure.

• The refrigerant is then compressed isentropically between States 2 and 3 and changes from a low-pressure vapor to a high-pressure vapor at State 3. The compression process causes the pressure to increase along with a corresponding temperature increase from TL to th.

• The refrigerant then passes through the condenser/ subcooler (States 3 to 4) where it changes from a superheated vapor to a subcooled liquid as heat is rejected to the warm air region. This process occurs at a constant high temperature and pressure.

Between States 4 and 1, the refrigerant undergoes an ideal expansion process in which the pressure is reduced and the refrigerant temperature returns to TL. An ideal or reversible engine is used for the expansion process.

Fig. 33-2 Diagram of Basic Refrigeration Cycle Processes.
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